#include <stdio.h>

int main () {

	/*member declaration*/
	double sidea;
	double sideb;
	double sidec;

	/* get data from user */

	printf("Enter sides for triangle\n");
	printf("Enter side A:\n");
	scanf("%lf", &sidea);
	printf("Enter side B:\n");
	scanf("%lf", &sideb);
	printf("Enter side C:\n");
	scanf("%lf", &sidec);

	// Check relations between different sides of the supposed triangle.
	// if all sides are equal, an equilateral triangle can be formed.
	// if only two sides are equal, an isoceles triangle can be formed.
	// if the sum of two sides are less than the third side, a triangle can not be formed.
	// if sides are different and the last condition is false, a regular triangle can be formed. 
	
	//check if can form a triangle
	if ((sidea + sideb) < sidec || ((sideb + sidec) < sidea)|| ((sidea + sidec) < sideb)){
			printf("This figure cannot be a triangle\n");
	}
	else if (sidea == sideb){
		if (sidea == sidec){
			printf("This is an equilateral triangle\n");
		}
		else {
			printf("This is an isosceles triangle\n");
		}
	}
	else if (sideb == sidec){
		printf("This is an isosceles triangle\n");
	}
	else {
		printf("This is a regular triangle\n");
	}
	return 0;

}